Oil and gas accumulations are found at depth in different geological basins worldwide. Exploration and production of such accumulations rely on the construction of a well according to a well plan.
Various well types exist and are defined according to usage such as wildcats or those used in exploration; delineation; and production and injection. Variations in well profile exist also according to vertical, slant, directional and horizontal trajectories. Each differs according to the oil company's objectives and the challenges that a given basin presents from the surface of the earth or the ocean to the hydrocarbon reservoir at a given underground depth.
Engineering challenges are related to the location of the well-site such as onshore or offshore, seawater depths, formation pressures and temperature gradients, formation stresses and movements and reservoir types such as carbonate or sandstone. To overcome these challenges, a highly detailed well plan is developed which contains the well objective, coordinates, legal, geological, technical, well engineering and drilling data and calculations.
The data is used to plot a well profile using precise bearings which is designed in consecutive telescopic sections—suface, intermediate and reservoir. To deliver the well objective and maintain the integrity of well over its lifecycle, a given wellbore with multiple sections and diameters is drilled from surface. Although there are many variants, a simple vertical well design could include a surface or top-hole diameter of 17½″ (445 mm), intermediate sections of 13⅝″ (360 mm) and 9⅝″ (245 mm) narrowing down to the bottom-hole diameter of 8½″ (216 mm) in the reservoir section.
Each consecutive section is ‘cased’ with the specified diameter and a number of metal tubes placed into the wellbore according to the length of the section. Each must be connected to each other after which they are cemented into the appropriately sized hole with a given tolerance. In this way, a well is constructed in staged sections, each section dependent on the completion of the previous section until the well is isolated from the formation along the entire distance from surface to the reservoir.
Scarcity of oil and gas is driving oil and gas companies to explore and develop reserves in more challenging basins such as those in water-depths exceeding 6,000 ft (1830 m) or below massive salt sections. These wells have highly complex directional trajectories with casing designs including 6 or more well sections. Known in the art as ‘designer’ or ‘close tolerance casing’ wells, these wells have narrow casing diameters with tight tolerances and have created a need to enlarge the wellbore to avoid very narrow diameter reservoir sections and lower production rates.
Therefore, the bottom-hole assemblies that are needed to drill these wells routinely include devices to underream the well-bore below a given casing diameter or other restriction. In this way, underreamed hole size has become an integral part of well construction and there is now an increased dependence on underreaming to meet planned wellbore diameters.
After underreaming, the underreamer is tripped out from the borehole and replaced by a calliper, which is an instrument for measuring the internal dimensions of the bore either mechanically, typically by means of extending fingers that contact the inside of the bore, or by acoustic or other echo-based sounding techniques.
Previously, the underreamer and calliper have been considered as two separate tools, each involved in distinct functions. Typically, an underreaming run could take 24 hours, after which a further 24 hours would be required for preparation of the calliper run. A further 24 hours could be taken in the calliper run before knowledge could be gained of actual wellbore diameters. The time-lag between underreaming and calliper measurements, therefore could easily exceed 48 hours depending on the depths involved. If the actual hole diameter did not match the planned diameter, casing tolerances would not be met and therefore a corrective run would be required and the whole cycle of underreaming and calliper measurements would need to be repeated.
In other applications such as tubular expansion casing or increased cementing thicknesses, the tolerances between the enlarged well-bore and the expanded tubular are very close. Variations of 1″ (25 mm) diameter can lead to the failure of the well construction activity.
Notwithstanding, the limitations of the prior art are overcome with the present invention, the wellbore construction process will continue to depend on given wellbore diameters for the placement of casing in a wellbore with a given tolerance which is determined by the required cementing thickness.
Consequently, where an undergauge (below tolerance) diameter goes undetected this would potentially jeopardize the wellbore construction activity. The present invention avoids this by measuring and verifying wellbore diameter and underreamer status and if either were insufficient, the tool performs automated diagnostics and may alert the user as required.
To those skilled in the art, it is known that underreaming generates uncertainty as to the activation status of the underreamer. This is because underreamers do not provide for clear activation status as described in Patent GB 2465505 which is incorporated herein as a reference.
The present invention is differentiated in this aspect as it provides for activation electronically as well as real-time verification of activation status by means of electronic signal which would enable a driller to activate a tool with certainty and eliminate reliance on hydra-mechanical activation. This would reduce time spent on activation as well as permit the exchange of data with the tool and surface.
The data may be transmitted in real-time by means of data transfer (mud pulse telemetry, fibre-optic or other) or maybe stored in memory and downloaded at a later time. The present invention would make underreamer status known in a clear manner and optimize underreaming operations thereby reducing failures and improving drilling efficiency and wellbore construction.
It is unsatisfactory to depend on indirect indicators such as whether cutter blocks are open or closed or whether fluid pathways are open and a pressure spike is seen at the rig floor to indicate activation. Such indicators do not provide actual measurements of the underreamed well-bore underreamed nor do they provide verification of underreaming erformance; they simply give information on the mechanical or hydraulic status of an aspect of the tool which may or may not lead to the desired well diameter.
To those skilled in the art, it is known that the industry relies on even more rudimentary and time-consuming indicators of verification such as an increase in drilling torque as cutters interact with the formation or even pulling up the drill-string and underreamer to the previous hole size in order to see whether the top-drive stalls as the bottom-hole assembly gets stuck due to the expanded tool. Or by drilling a pilot hole section with the underreamer deactivated and pulling back into the pilot hole.
Therefore, the prior art does not lend itself to a reliable or certain means of measuring and verifying underreamed wellbore diameters in real-time or memory mode.
Further the prior art perpetuates drilling inefficiencies due to the uncertainty of the actual status of the underreamer.
Further the prior art generates time-consuming cycles of entry and exit into the well-bore.
Further the prior art relies on pressure restrictions or weight for activation.
Further the prior art does not detect variations in well-bore in real-time.
Further the prior art does not automatically troubleshoot undergauge hole or malfunction.